This invention relates to silicon nitride-based, shaped ceramic bodies having high resistance to heat, oxidation and wear and excellent mechanical strengths and high modulus.
Silicon nitride has been attracting much attention for its favorable properties, and the research thereof has recently led to remarkable developments. It has been already utilized for a wide variety of applications such as for the production of cutting tools, mechanical seals, etc., for its resistance to at and wear, and will find wide use for bearings, turbosupercharger rotors, etc., in the near future. It will play an important role in the production of gas turbine blades, adiabatic engines, heat exchangers for high-temperature gas furnaces and other equipments which are operated under very severe conditions.
Among various shaped bodies, fibers of silicon nitride can effectively excellent properties inherent to silicon nitride, such as mechanical strength, resistance to heat, impact, oxidation and chemicals, electrical insulation, and wettability with metals. The silicon nitride fibers have another advantage of being more amenable to molding. Economic production of the fibers, therefore, will open up new areas into which silicon nitride can make inroads. More specifically, silicon nitride will be used as a heat-resistant material for mesh belts, conveyor belts, curtain and filters, or as a reinforcing material in various composite materials for engine parts, fan blades and aircraft structures when the fibers are processed into woven fabrics, felts, ropes, yarns or chopped strands.
The following shaped ceramic bodies have been hitherto proposed:
(1) Shaped bodies formed of a homogeneous mixture of silicon carbide and silicon nitride obtained by calcining an organosilazane produced by reaction of a halogenosilane with ammonia (Japanese Published Unexamined Patent Applications Nos. 49-69717, 49-20206 and 62-202863 and U.S. Pat. No. 4,482,669);
(2) Shaped bodies of Si-N-O or Si-N-O-M series obtained by calcining perhydropolysilazane or metallopolysilazane (Japanese Patent Application No. 63-46966 and U.S. Pat. No. 4,397,828);
(3) Shaped bodies of Si-C containing ceramics obtained by calcining polycarbosilane (Japanese Published Unexamined Patent Applications Nos. 53-93314, 54-3815 and 54-16521); and
(4) Shaped bodies of Si-Ti-C or Si-Zr-C series obtained by calcining polytitanocarbosilane or polyzirconocarbosilane.
The known shaped ceramic bodies have the following defects. The shaped bodies (1) above contain a large amount of free carbon because of a high carbon content in the raw material. This causes phase separation or reaction when subjected to a high temperature, resulting in deterioration of inherent properties of silicon nitride and silicon carbide, especially lowering of electrical insulation, strengths and resistance to thermal shock. The shaped bodies (2) show poor mechanical strength at high temperatures, though they have good mechanical strength at room temperature. The shaped bodies (3) and (4) require an infusiblization treatment during the course of the production process thereof, since the raw materials are melted when heated. Thus, the process becomes complicated. Additionally, the infusiblization treatment is susceptible to contamination by oxygen, resulting in lowering of mechanical strengths and resistance to heat.